Of tool materials, cutting tools receiving severe force or heat at their edge portions in particular are required to have the following material properties:
1. To have a high hardness at high temperatures. PA1 2. To have a toughness especially at high temperatures. PA1 3. That they are chemically stable and do not react at their edges with work, i.e., material to be cut.
Alumina base tool materials now finding use as cutting tool materials meet entirely the required properties 1 and 3, but offer a problem in connection with the property 2. Al.sub.2 O.sub.3 -TiC base ceramics have been developed so as to overpass such a limit. The ceramics of such a system introduce epoch-making improvements in the Al.sub.2 O.sub.3 base materials, and are a typical and successful example of composite ceramics. However, since they are a composite of oxides and carbides, difficulty is involved in the densification thereof by simply applying heat. It is then required to take a certain measure so as to prohibit the generation of gases between the Al.sub.2 O.sub.3 particles and the associated dispersive particles (TiC) to an extreme extent. Typical of the industrial production techniques for stably making the products of high quality are hot pressing (hereinafter referred to as "HP") whrerein mechanial force is applied together with heat, and hot isostatic pressing (hereinafter reffered to as "HIP") wherein large and uniform forces are applied from the entire circumference of the body to be pressed. Such Al.sub.2 O.sub.3 -TiC base ceramics are characterized by good wear resistance and low affinity to iron, and so enjoy wide use in the precision finishing or high-speed cutting of cast iron.
Now, very high cutting speed is being demanded so as to achieve higher productivity in various fields such as automobile or aircraft industries. On the other hand, machine tools coping with such high cutting speed have been developed.
With the progress of unmanned production lines, it is required to enhance the reliability of tools, inter alia, ceramic tools.
In order to achieve high-speed cutting and improve the reliability of cutting tools, it is required to further improve the performance, especially, toughness of currently available Al.sub.2 O.sub.3 -TiC base ceramics.
As one means for improving toughness, consideration is given to the enhancement or reinforcement of the interfaces of the TiC particles per se and the Al.sub.2 O.sub.3 particles per se, or those between the TiC particles and the Al.sub.2 O.sub.3 particles. In the past, the addition of TiO.sub.2 (JP Patent Kokoku-Publication No. 51-569) or Ti (JP Patent Kokoku-Publication Nos. 50-20968 and 50-39445) was attempted for that purpose.